I don't think that there is any rule; neither or both words can be fitted into the grammar of the sentence.
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RegardsHi,Hi,
It sounds informal. I assume these may sound better:
Whether or not it rains today, we will play soccer.
Whether or not he is rich, he is a successful person.
Regards
RegardsI can't find the word 'wrong' in it.Nor in mine, MeggPhaggSioux. What am I, chopped liver?